1. Field of the Invention
The present invention relates to a process for preparing fine-particulate metal hydroxide comprising aluminum hydroxide as a major component and fine-particulate metal oxide comprising aluminum oxide as a major component. More precisely, it relates to a process for preparing fine-particulate metal hydroxide comprising aluminum hydroxide as a major component and fine-particulate metal oxide comprising aluminum oxide as a major component, having high industrial productivity and no tendency of producing coarse particles.
2. Description of the Related Art
Hydrolysis reaction of metal alkoxides has been the subject of growing interest as a method for preparing a sol, a gel and fine particles for precursors of ceramics in view the following advantages:
(1) the metal alkoxides are easily hydrolyzed at room temperature to produce metal hydroxides, and
(2) there is no possibility that the product is contaminated with anions as impurities, and a number of reports on said reaction have been published [see, for example, Amer., Ceram. Soc. Bull., 54, 286 (1975) and Nippon Ceramics Kyokai Gakujutsu Ronbunshi, 99 (10), 1036-1046 (1991)).
When a silicon alkoxide or a titanium alkoxide is used as the starting material, monodispersed spherical particles of uniform particle size containing no coarse particles can easily be obtained by hydrolysis (see, for example, J. Colloid Interface Sci., 26, 62 (1968) and J. Am. Ceram. Soc., 65, C199 (1982)). However, when an aluminum alkoxide is used as the starting material, colloidal gel or gel-form precipitate tends to be formed due to its higher hydrolysis reaction rate. Therefore, it has been considered that the production of monodispersed particles of uniform particle size without containing coarse particles is difficult.
Metal oxide comprising aluminum oxide as a major component, produced by calcining powdered metal hydroxide comprising aluminum hydroxide as a major component, is a material which has been widely used as a raw material for sintering and as various kinds of fillers. It is desirable to produce a metal oxide comprising aluminum oxide as a major component, which has a narrow particle size distribution and can be easily dispersed, in order to obtain excellent properties.
In the synthesis of aluminum hydroxide by hydrolysis of an aluminum alkoxide, several inventions and researches have been made to prepare monodispersed fine particles under certain specific conditions (JP-A-Sho 62-158116 and J. Am. Ceram. Soc., 74, 2263 (1991)).
Those approaches use the hydrolysis reaction at a low concentration of the raw material in a reaction medium to which a solvent other than the alcohol constituting the aluminum alkoxide is added. While the monodispersed particles containing no coarse particle may be produced by those processes, productivity is low in industrial production.. Further, the alcohol used as the solvent must be purified before it is recycled to the synthesis of aluminum alkoxide.
In addition, as aluminum oxide having a narrow particle size distribution, aluminum oxide produced by vapor phase hydrolysis in which anhydrous aluminum chloride is evaporated and combustively hydrolyzed in an oxyhydrogen flame, has been known.
The aluminum oxide produced by this method suffers from a drawback that, when used as various kinds of fillers, it is corrosive due to the presence of an inevitable chlorine component as an impurity.
Further, particulate aluminum oxide produced by pulverization, milling, grinding or the like of aluminum oxide containing coarse particles also suffers from a drawback that it has a broad particle size distribution and is susceptible to reagglomeration.